1. Field of the Invention
This invention concerns a dispersion agent for cement or blended cement materials and, more specifically, it relates to a cement dispersion agent capable of greatly improving the workability of concretes, mortars or pastes as the hydraulic cement blends thereby improving the applicability and the operationability thereof or to a cement dispersion agent capable of highly decreasing the unit amount of water and obtaining high strength.
2. Description of the Prior Art
Chemical admixtures that have usually been employed so far can include lignin sulfonic acids (salts thereof), oxycarboxylic acids (salts thereof), polycarboxylic acids (salts thereof), naphthalene sulfonic acid--formaldehyde condensates (salts thereof), and melamine sulfonic acids--formaldehyde condensates (salts thereof).
Among them, naphthalene sulfonic acid-formaldehyde condensates (salts thereof) and melamine sulfonic acid-formaldehyde condensates (salts thereof) have been used as chemical admixture causing less delay in curing, no air entrainment and having high dispersibility.
However, the dispersibility of them at an addition amount of less than 0.2% by weight to cements (in a low addition region) is considerably lower than that of sulfonic acids (salts thereof), oxycarboxylic acids (salts thereof), polycarboxylic acids (salts thereof) and the like. They are not used for raw concretes of medium to low strength or concrete plant products from an economical point of view. While on the other hand, their dispersibility at an addition amount of greater than 0.4% by weight to cements (in a high addition region) is equal to or greater than than that of the above-mentioned chemicals. Further, since they also have a feature of causing less delay in the curing and with no air entrainment even in the high addition region, they have been used for raw concretes at high strength or concrete plant products. However, a further improvement in the dispersibility is desired from an economical point of view. For the further improvement of the dispersibility without giving the undesired effects of delay in the curing and air entrainment, there has been been reported a separation method (refer to Japanese Patent Laid-Open No. Sho 58-176158 ), oxidizing treatment (refer to, for example, Japanese Patent Laid-Open No. Sho 60-33239), etc.
However, the dispersibility can not be improved as expected by merely controlling the molecular weight distribution by removing the high molecular weight portion and/or low molecular weight portion by the separation method. Further, since the materials removed by the method have no effective application uses, this method is disadvantageous also from an economical point of view. Further, although the introduction of carboxylic groups into sulfonic acid type compounds through oxidation is an effective method of improving the dispersibility, control of the molecular weight distribution by which the low molecular weight portion, with less effect for the improvement of the dispersibility, is converted into a higher molecular portion can not be attained merely by oxidation.
As described above, it has been impossible to control the distribution of the molecular weight while introducing, at the same time, carboxylic groups for further improving the dispersibility without giving the undesired effects of delaying curing and causing air entrainment. The present inventors have made a further study on a method capable of controlling the molecular weight effective for the improvement of the dispersibility by merely conducting the chemical reaction without effecting the separating operation as in the prior art method and which is capable of moderately introducing carboxylic groups effective to the improvement of the dispersibility and have arrived at this invention.